Centering tail piece?

[tundrawolf]

I saw a video on youtube on how to center a tail stock (tail piece?)

What I am trying to do is weld two tubes together perfectly concentric, and hold them tightly together with the tail stock, maybe start with two tacks. I have no idea if it will be able to endure the strain that a weld causes. The tubes are about 5/*" diameter, thin wall, mild steel, and the total part is less than 3" long.

Apparently I need to fabricate a tool that holds a rod in the chuck of the lathe, with a hold drilled through it's center for another rod, that holds the smaller dial indicator (Which I have)

How do you guys center your tail piece?

 

[Ulma Doctor]

to get the tailstock in alignment, you can make or buy a test bar.
take a piece of stock , 12" or longer and 1 or 2" in diameter, but 3/4" would work too
face and centerdrill both ends of the stock to accept a center
put the bar between centers and note the indicated concentricity, by rotating the work by hand
if the bar runs fairly concentric, you can do a rough alignment by putting the indicator in the toolpost or on the compound rest or saddle.
run the indicator towards the tailstock and note the indicated offset near the far end of the bar- this is the rough offset.
ideally you'll have zero offset, and won't cut a taper- but sometimes that is another rabbit hole
you can then add a drive dog to the test bar and take a skim cut at the tailstock end and then repeat the cut near the headstock
that will give you the real offset.
you'll then correct the tailstock until the same cut results in equal diameters on both ends.
then you'll have true zero offset.
make sure your lathe is leveled before you try the experiments!

 

[Wreck™Wreck]

Machine After Welding, nothing that you do will be "Perfectly Concentric" after welding. If one were to produce said product from bar stock in one setup it would still have errors that you can not control. The closest that you will get will be by using a cylindrical grinder and you will not achieve zero error there. I hope this helps (-:

 

[Ray C]

There are many ways to do it but, here's what I do when I suspect my tail-stock has moved. Put a sharp tip on a short piece of scrap then, put a center in the tail-stock. Move the two together and adjust tail-stock until the points line up horizontally (as looking from the top down toward the bed). This will get you in the ballpark. Now take a long scrap bar about 12" long and 1.25 to 1.5" dia and center drill both ends. Spin the piece between centers and make light passes of about 10 thou or so. Measure the diameters of the bar 1.5" away from the ends. Make adjustments in the tail-stock until your diameters are the same (or within your level of desired accuracy).

Something to keep in mind.... The TS end of a cut is often larger in diameter than the chuck end. This is because the tail-stock ram and live center push away under pressure. This causes the cut depth to be decreased and the part is larger at the tail-stock end. As the cut travels, the stronger hold of the "immovable" spindle keeps the shaft in place and the depth of cut increases and the part tapers down to a smaller diameter.

There are other ways... I'm just tell you what I do when I need to spot check. There's also a method where you use a long rod with metal "donuts" on each end. You take the same cut on both donuts and measure their diameter.

One thing for sure, lining up tailstock centering by eye or with an indicator will get you nowhere because, they all push away a little bit under pressure. Heavier cuts push away more than light cuts. You need to get to know your lathe well enough to know what you can get away with and still hold a straight line and not make tapers. FWIW, my lathe will stay within 0.0003 over 10" if it's dialed in and if I'm paying attention.


Regards

Ray C.

 

[Ray C]

One other thing, you need to spin between centers. If you hold a piece firmly in the jaws of a chuck, the piece is not free to self-center with the tip on the tailstock. There are some tricky ways to get around this but it's not a sure bet.

Ray C.

 

[tundrawolf]

I tried cutting a probably 5/8" metal rod smooth so I could turn it into that measuring device. The guy on youtube made it look effortless, but I tried and tried, even with carbide (I know it rhymes) and it's still 10/1000 off. Chattery and rough and ugly finish.

He makes it look like you just have to press a button and the chips come flying off perfectly, the work has a nice shiny finish, and everything is perfectly concentric. Elves are singing, somewhere.

I am so frustrated right now. This is harder than wrestling with wolves. (But less dangerous I assure you)

 

[tundrawolf]

Machine After Welding, nothing that you do will be "Perfectly Concentric" after welding. If one were to produce said product from bar stock in one setup it would still have errors that you can not control. The closest that you will get will be by using a cylindrical grinder and you will not achieve zero error there. I hope this helps (-:

And I'm working with an Aerospace engineer/machinist who is also dating my mom -_- Can it get any worse? He wants to see my lathe tomorrow ;_;

 

[Wreck™Wreck]

Sounds like a personal problem (-:

 

[tundrawolf]

Sounds like a personal problem (-:

It is. It really is.

;_;

 

[Ray C]

And I'm working with an Aerospace engineer/machinist who is also dating my mom -_- Can it get any worse? He wants to see my lathe tomorrow ;_;

In all honesty, you completely lost me with the discussion of welding 2 pipes in a lathe using the TS for pressure. Upon reading that, I posted up lengthy (but hopefully clear) description of a cheap/dirty way to align the TS before you damaged your lathe.


Ray